This proposal requests funding for an EPR Spectrometer operating at both 9 and 35 GHz equipped with variable temperature accessories. This equipment would replace an EPR system purchased in 1974 from Varian that can no longer be maintained since Varian discontinued manufacturing EPR spectrometers. The principal investigator has used EPR methods as an integral part of his research program since 1971 and has several ongoing funded NIH projects that require this equipment. Both Drs. Benkovic and Hamilton (co-investigators) have studied structure and function of several metalloenzymes and EPR equipment is essential for continued progress on their funded NIH grants.